The present invention relates generally to crossbow bowstring drawing mechanisms. More particularly, the present invention relates to a crossbow bowstring drawing mechanism which may be integrated into a crossbow. The bowstring drawing mechanism may utilize either an integrated or external power source, such as a manually operated crank or motor, to draw the bowstring to its "cocked" or firing position. The mechanism may also be used to release the bowstring from the firing position and relieve the tension on the crossbow limbs.
Traditional archery devices have normally included a bow having two outwardly extending arms or limbs and a bowstring strung between the ends of the limbs. In order to shoot a projectile, such as an arrow, the user grasps the bow in approximately the center between the two outwardly extending arms and pulls back or "draws" the bowstring with one hand while at the same time pushing the bow away with the other hand. Drawing the bowstring requires a certain amount of strength and can, over time, take a physical toll on the user's arms. The amount of force needed to draw a given bow is normally measured in pounds and is known as the "draw weight" of a bow. Upon release of the bowstring from this "drawn" position, potential energy in the bowstring is imparted upon the projectile and the projectile is propelled or "fired".
One commonly used technique of increasing the speed and accuracy at which a projectile is propelled is to increase the stiffness of the outwardly extending bow limbs. However, if this is done, the pulling or "drawing" of the bowstring into position for "firing" requires more effort. At some point, simply increasing the stiffness of the outwardly extending bow arms becomes counterproductive since users do not have the physical strength to pull back or "draw" the bowstring into position for firing and maintain this position until the user has sighted his or her target and is ready to release the bowstring. Furthermore, if the user is struggling to maintain the "drawn" position of the bowstring, his or her aim will be negatively affected.
Crossbows were developed to assist the user in holding the bowstring in the "drawn" position and relieve the tension applied to users' arms when holding the bowstring in the "drawn" position while sighting a target. In a crossbow, a longitudinally extending main beam, commonly called the stock member, includes a trigger mechanism which holds the crossbow bowstring in the drawn position, allowing the user to sight a target without manually holding and maintaining the draw weight. This allows the stiffness of the bow limbs to be increased significantly, and modern crossbows can have bowstring pull weights of 150 pounds or more. Although the trigger maintains the drawn position of the bowstring, drawing the bowstring into engagement with the trigger mechanism is still very difficult. It is readily apparent that with high pull weights, even operating a crossbow could be difficult, if not impossible, for many users having limited physical strength. This is particularly true for target practice or other situations where the crossbow is cocked numerous times.
In order to draw the crossbow bowstring and "cock" the crossbow, the user must have sufficient physical strength to draw the full bowstring draw weight of the bow. Devices have been used in conjunction with crossbows to make this "cocking" operation easier for users to accomplish. For example, some crossbows include a stirrup bracket mounted on one end of the crossbow. In such crossbows, the user places the stirrup bracket onto the ground and places a foot in the stirrup bracket. By applying the user's body weight to the grounded stirrup bracket, the user can "draw" the crossbow bowstring into "cocked" position. Although helpful, this provides only limited advantage. In addition, it is very difficult to properly draw the bowstring in a manner that the limbs are each tensioned to the same degree, or the bow is drawn in a balanced manner.
Manual crank winch devices are also known which draw the crossbow bowstring into the cocked position. However, such devices are often large, heavy and cumbersome and must be connected and disconnected from the crossbow with each use. Furthermore, crossbows using leverage type "cocking" devices are known. Such crossbows typically have an arm which is pivoted to pull or push the crossbow bowstring into the cocked position. Various other arrangements to cock the bowstring have also been developed, including relatively complex devices utilizing pulley systems mounted to the frame of the crossbow.
None of these known arrangements have provided a system which easily and repeatably enables cocking of the crossbow bowstring in a cost effective integrated arrangement.
Another significant problem with respect to cocking of a crossbow bowstring as briefly mentioned above, whether performed manually or by means of a bowstring drawing mechanism such as described in known mechanisms above, is found in properly drawing the bowstring relative to the outwardly extending limbs of the crossbow such that when the bowstring is released from the crossbow trigger mechanism, an equalized force will be imparted to the projectile or arrow positioned therein. This balancing of the forces imparted on the bowstring by means of the crossbow limbs is particularly important for shooting accuracy in using the crossbow, and also adds to safety of use. It should be recognized that cocking the crossbow will many times result in uneven balancing of tension applied to each of the crossbow limbs, even if known cocking devices as described above are used. Further, although these known systems described above attempt to simplify the bowstring cocking procedure, in many cases the mechanisms add complexity or cost, or are cumbersome to handle and use effectively. None of the known arrangements provide an easy and effective system which automatically draws or releases a bowstring into or form a cocked position. Additionally, it would be desirable to be able to effectively retrofit a crossbow with a cocking mechanism.